Method of oil and gas recovery from previously used wells

ABSTRACT

A method of oil and gas recovery from previously used oil or gas containing wells includes selecting at least two previously used oil or gas wells located in an area of a same oil or gas containing layer and designating one the previously used oil or gas wells as a production well and another of the previously used oil or gas wells as an injection well, cutting in the injection well slots which communicate the injection well with the oil or gas containing layer, injecting a fluid into the injection well after cutting the slots in the injection well to increase a pressure in the production well, and subsequently recovering oil or gas from the production well.

CROSS-REFERENCE TO A RELATED APPLICATION BACKGROUND OF THE INVENTION

The present invention relates to oil and gas excavation, and in particular it relates to methods for oil and gas recovery from oil and gas containing layers in previously used wells.

It is known that in previously used oil and gas wells oil or gas pressure of remaining oil and gas is low and does not allow efficient recovery of oil and gas from them. In order to increase the oil and gas pressure in oil and production wells it was proposed to inject fluids into a neighboring injection well which communicates with the production well via a production layer of oil or gas, so as to increase the oil or gas pressure in the production layer and as a result to increase the oil and gas pressure in the production well to improve its production output.

It has been determined that is desirable to improve this known method in order to further increase the efficiency of recovery of oil or gas from the previously used oil or gas wells.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a method of oil and gas recovery from previously used oil and gas wells, which is a further improvement of known methods of oil and gas recovery.

In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, a method of oil and gas recovery from previously used oil or gas wells, which includes selecting at least two previously used oil or gas wells located in an area of a same oil or gas containing layer, designating one the previously used oil or gas wells as a production well and another of the previously used oil or gas wells as an injection well, cutting in the injection well slots which communicate the injection well with the oil or gas containing layer, injecting a fluid into the injection well after cutting the slots in the injection well to increase a pressure in the production well, and subsequently recovering oil or gas from the production well.

When the method of oil and gas recovery from previously used oil and gas wells is carried out according to the present invention, a recovery of oil or gas from the production well can increase 10-20 times.

According to a further feature of the present invention, a plurality of oil or gas wells communicating with the same oil or gas production layer can be used as production wells, from which the recovery of oil or gas can be increased as a result of cutting in the injection well slots which communicate the injection well with the oil or gas containing layer, and injecting a fluid into the injection well after cutting the slots in the injection well to increase a pressure in the plurality of the oil or gas production wells.

According to a further feature of the present invention, after cutting the slots in the injection well, a hydro-fracturing is carried out in the injection well, which further increases the pressure in the previously used oil or gas wells productions wells after injecting of fluid into the injection well and as a result further increases the efficiency of oil and gas recovery from the previously used oil or gas production wells.

According to a further feature of the present invention, slots are also cut in the oil or gas production well or wells, which improves communication of the oil or gas production wells with the oil or gas containing layer.

According to a further feature of the present invention, after cutting the slots in the oil or gas production well or wells, a hydro-fracturing is carried out in the production well or wells, which further improves communication of the oil or gas production well with the oil or gas containing layer.

According to a further feature of the present invention, the fluid which is used for supplying into the injection well can be a water taken from the injection well and/or the production well.

The novel features of the present invention are set forth in particular in the appended claims.

The invention itself will be best understood from the following detailed description of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a method of oil and gas recovery from oil and gas containing layers in previously used wells according to the present invention, first at least two previously used oil or gas wells located in an area of a same oil or gas containing layer, are selected for implementation of the method. Usually these are the old wells in which cumulative perforation was utilized to recover oil or gas from oil or gas containing layers.

For implementation of the method according to the present invention, one the previously used oil or gas wells is designated as a production well and another of the previously used oil or gas wells is designated as an injection well, for conducting subsequent procedures of the new method of gas or oil recovery as will be explained hereinbelow.

In a subsequent step, slotting of the wall of the oil or gas injection well is carried out to eliminate the annular stress ring of rock and exclude the influence of a rock pressure and to communicate it with the oil or gas containing layer. Slot-shaped cavities which are produced by the slotting remove annular compressive stresses, thereby increasing the subsequent outflow of fluid from the injection well. It is desirable to produce four slots with a width which is not less than two diameters of the well, extending along the whole height of the oil or gas containing layer but not less than ten diameters of the well, and having a thickness not less than three cm. The slotting can be carried out by hydraulic sand-blasting, or disc-shaped tools. In order to exclude influence of deep horizontal stresses, slots can be also used, which are oriented perpendicular to the direction of horizontal stresses.

Then in the method according to the present invention a hydraulic fracturing can also be carried out in the injection well. This can be achieved for example by a hydraulic action, including pumping of liquid under high pressure. It is possible for this purpose to pump liquids which contain sand and/or other particles, to provide cutting by rotating tools, etc. As a result of this, existing cracks are opened and new cracks are formed in surrounding rock. With additional pumping-in of a mixture of liquid and sand, the cracks are expanded or wedged out with maintaining of a high ability for passage of water from the injection well.

In the next step of the method according to the present invention a fluid is supplied into the injection well, in particular water injected under pressure as known in the art. It applies pressure to the oil or gas containing layer, and correspondingly a pressure in the oil or gas production well is increased. Oil or gas is then recovered from the oil or gas production well in a known way with significantly increased quantities. As a result of the method according to the present invention the recovery of oil or gas from the oil or gas production well can be increased 10-20 times.

The water which is used for injection into the injection can be a water from the injection well and/or water from the production well. In this case no additional sources for delivery and supply of water for introduction into the injection well are needed.

In the method of the present invention some steps implemented in the injection well can be also implemented in the oil or gas production well with same or different parameters. In particular slots can be also cut in the oil or gas production wells, which improves recovery of oil or gas from the oil or gas production well. Also after cutting the slots in the oil or gas production well, a hydro-fracturing can be carried out in the oil or gas production well, which further improves recovery of oil or gas from the oil or gas production well.

In the further implementation of the present invention, a plurality of oil or gas wells communicating with the same oil or gas production layer can be used as production wells. The recovery of oil or gas can be increased in this case from the plurality of oil or gas wells communicating with the same oil or gas production layer, cas a result of cutting in the injection well slots which communicate the injection well with the same oil or gas containing layer, and injecting a fluid into the injection well after cutting the slots in the injection well to increase a pressure in the plurality of the oil or gas production wells.

The present invention is not limited to the details which are explained hereinabove, since various modifications and structural changes are possible without departing from the spirit of the invention. 

What is desired to be protected by Letters Patent is set forth in the appended claims:
 1. A method of oil and gas recovery from previously used oil or gas containing wells, comprising the steps of: selecting at least two previously used oil or gas wells located in an area of a same oil or gas containing layer; designating one of the previously used oil or gas wells as a production well and another of the previously used oil or gas wells as an injection well; cutting by disc-shaped tools four slots in the injection well which extend uninterruptedly over the whole height of the oil or gas containing layer and communicate the injection well with the oil or gas containing layer uninterruptedly over the whole height of the oil or gas containing layer; carrying out a hydro-fracturing in the injection well; cutting in the production well slots with same parameters as in the injection well; carrying out a hydro-fracturing in the production well; injecting a fluid into the injection well after cutting the slots in the injection well to increase a pressure in the production well; using as the fluid for supplying into the injection well a water taken from the injection well and/or the production well without using additional sources for delivery and supply of water for introduction into the injection well; and subsequently recovering oil or gas from the production well. 2.-6. (canceled) 